The proposed work in the coming year will be concerned primarily with the effects of hormones on pyrimidime nucleotide metabolism in heart and skeletal muscle. We have observed that in rat diaphragm incubated in vitro insulin causes an increase in the tissue content of UTP. This action insulin appears to be a consequence of the stimulation by the hormone of the enzyme uridine kinase that catalyzes the phosphorylation of uridine to form UMP. That uracil nucleotide metabolism is influenced by diabetes is indicated by the finding that the UTP content of heart and skeletal muscle is decreased in streptozotocin-diabetic rats. Efforts are now being made to study uridine kinase in muscle from normal and diabetic animals and to obtain information about the properties of the enzyme. Other studies in our laboratory include investigations of the metabolic effects of lithium ions and catecholamines in tissue preparations in vitro.